Dr. Rolls and colleagues have the novel idea of manipulating memories not during wake but instead during sleep. Some of the most commonly used treatments for PTSD and other disorders triggered by traumatic or painful memories seek to modify the response to such memories, rendering them harmless or less likely to cause pain. One popular method, called extinction therapy, calls for the patient to recall the fearful memory in a safe environment such as a therapist’s office, and to learn to make new associations with the memory, which can have the effect of de-activating the memory as a “trigger.”

Extinction therapy has the disadvantage of making the patient recall, and to varying extents, relive the trauma. As explained in a paper published today in Molecular Psychiatry, Dr. Rolls and colleagues base their alternative approach on prior research showing that memories are routinely consolidated and strengthened during sleep. Using mice conditioned to feel fearful when exposed to a cue―in this case a particular chemical odor―they wanted to see if they could weaken the fear memory while the animals were sleeping.

The researchers succeeded in both strengthening the fear memory, and in an accompanying set of experiments, weakening that same memory. The latter was accomplished by taking the mice already conditioned to experience fear when the odor was introduced in their cage, and to inject them with a substance called protein synthesis inhibitor or PSI. PSI, which blocks natural processes that build new proteins, was injected into a portion of the amygdala, a brain area known to be central in processing fear memories. Inferring from the animals’ behavior, the experiment succeeded; the fear memory trace was weakened.

“We see this as proof of concept that memories can be manipulated during sleep and that such manipulation offers diverse therapeutic potential. We must remember that there is still a long way to go until such therapy can be applied to humans. There are many challenges ahead,” Dr. Rolls and colleagues said. But among the potential benefits is that the actual memory behind the fear seems to be capable of being changed, not merely attached to a “safer” set of associations. Also, if proven adaptable for humans, patients would not have to re-experience the fear in order to “work” on it with a therapist, the researchers said.

Article comments

The fact that the mice were injected with a substance leads me to believe that some form of medication is being considered. There are proven methods of treatment that are drug free. Why go the medication route?

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